1. Technical Field
Embodiments of the subject matter disclosed herein relate to hybrid generator-battery systems and methods. Other, embodiments of the subject matter disclosed herein relate to control methods providing fuel savings for hybrid generator-battery systems.
2. Discussion of Art
Battery applications are typically divided into two categories, backup and hybrid. The backup category relates to applications in which the battery is used as a backup power source in case of main power source failure. The hybrid category relates to applications in which the battery undergoes continual (or in some cases, periodic) charge and discharge operation in concert with a main power source.
Telecom operators in areas where grid power is unavailable or only intermittently available have relied on diesel generators to power base transceiver stations (BTS). While inexpensive to install, the escalating cost of diesel fuel, and its delivery to remote locations, has driven the search for alternative solutions with lower total cost of ownership. Fuel usage can be dramatically reduced by use of a diesel-battery hybrid power system. In such a scenario, a long life cycle battery is used to alternately share the load with the diesel generator. The diesel generator is modulated on and off and, when it is active, powers the BTS and recharges the battery at an overall higher efficiency than if powering the BTS only. Once the battery is recharged, the generator can be turned off and the battery is used to sustain the BTS load. Fuel savings of up to 50% have been achieved in some applications. Such hybrid systems may be used in other stationary power applications as well such as, for example, mining operations. Reduced fuel consumption directly impacts the operational expenditures of telecom sites and cuts greenhouse gas emissions. Hybrid systems may also be applied in mobile applications such as automobiles where an onboard generator is cycled on and off to maintain the charge or energy state of a battery. Other stationary or mobile applications are possible as well.
For typical engine and generator sets used in telecom base stations, as the load fraction increases so does the efficiency of the engine and generator set. Load fraction=battery recharge power plus the base load divided by the rating of the generator source. Therefore, fuel savings is proportional to base load times battery discharge event time energy discharged divided by the sum of battery discharge event time plus battery recharge event time.
Even with the success of the hybrid generator-battery systems in reducing fuel costs, it is still desirable to further improve fuel savings over the potential life of the equipment in such hybrid generator-battery systems.